Vilma Buršíková

Deposition of thin organosilicon polymer films in atmospheric pressure glow discharge

The atmospheric pressure glow discharge burning in nitrogen with small admixture of organosilicon compounds such as hexamethyldisilazane or hexamethyldisiloxane was used for the deposition of thin organosilicon polymer films. The properties of the discharge were studied by means of optical emission spectroscopy and electrical measurements. The deposited films were characterized by atomic force microscopy, x-ray photoelectron spectroscopy, infrared transmission measurements, ellipsometry, depth sensing indentation technique and contact angle measurements. The films were polymer-like, transparent in the visible range, with uniform thickness and without pinholes. The film hardness varied from 0.3 to 0.6 GPa depending on deposition conditions, the elastic modulus was in the range 15-28 GPa and the surface free energy was in the range 26-45 mJ m-2. The studied films exhibited good adhesion to the substrate.

Surface modification of polyethylene and polypropylene in atmospheric pressure glow discharge

An atmospheric pressure glow discharge (APGD) was used for surface modification of polyethylene (PE) and polypropylene (PP). The discharge was generated between two planar metal electrodes, with the top electrode covered by a glass and the bottom electrode covered by the treated polymer sample. The discharge burned in pure nitrogen or in nitrogen–hydrogen or nitrogen–ammonia mixtures. The surface properties of both treated and untreated polymers were characterized by scanning electron microscopy, atomic force microscopy, surface free energy measurements and x-ray photoelectron spectroscopy. The influence of treatment time and power input to the discharge on the surface properties of the polymers was studied. The ageing of the treated samples was investigated as well. The surface of polymers treated in an APGD was homogeneous and it had less roughness in comparison with polymer surfaces treated in a filamentary discharge. The surface free energy of treated PE obtained under optimum conditions was 54 mJ m−2 and the corresponding contact angle of water was 40°; the surface free energy of treated PP obtained under optimum conditions was 53 mJ m−2 and the contact angle of water 42°. The maximum decrease in the surface free energy during the ageing was about 10%.

Plasma modification of polycarbonates

Abstract We deposited protective coatings on polycarbonates from hexamethyldisiloxane (HMDSO) and HMDSO/O2 mixtures by the plasma enhanced CVD method. In particular, we studied deposition rate, optical constants in UV/VIS, film composition and mechanical properties dependent on rf power and oxygen to HMDSO flow rate ratio. Plasma polymer HMDSO films (PP-HMDSO) showed good transparency in the visible and increased absorption in UV region. The optical constants of HMDSO/O2 films were similar to the tabulated SiO2. In general, the films were characterised by a relatively high content of hydrogen (22–66%) and a carbon content below 20%. The films deposited at an oxygen-to-HMDSO flow rate ratio higher than 15 exhibited higher tensile stress and higher hardness than those prepared at ratios of 5–10. The nature of the internal stress changed to compressive for PP-HMDSO. Plasma pre-treatment of polycarbonate in argon significantly improved the film adherence, especially when low powers and short treatment times were used.

Temperature dependence of mechanical properties of DLC/Si protective coatings prepared by PECVD

One of the main problems of amorphous diamond-like carbon (a-C:H or DLC) films deposited by plasma-enhanced chemical vapor deposition (PECVD) is their poor thermomechanical stability. The thickness of the films is limited to a few hundreds of nanometers in order to guarantee stable coatings. It is shown that major improvements in the mechanical properties of DLC films can be obtained if hexamethyldisiloxane is added in the gas mixture used for DLC deposition. The mechanical properties of hard protective DLC/Si films deposited by PECVD from an argon-methane-hexamethyldisiloxane mixture have been analyzed using microindentation techniques as the main experimental characterization tool. The formation and development of crack lines and patterns have been studied in order to determine the fracture toughness of the film and of the interface as a function of temperature.

Deposition of protective coatings in rf organosilicon discharges

The paper discusses the deposition of protective coatings ranging from organosilicon plasma polymers to SiO2-like films and hard diamond-like carbon/silicon oxide (DLC?:?SiOx) coatings in radio frequency capacitively coupled discharges using hexamethyldisiloxane (HMDSO). As a result of the optimization of the deposition conditions it was possible to obtain high performance protective coatings. In the HMDSO/O2 mixture, it was shown that rather than the SiO2-like film a hard cross-linked SiOxCyHz polymer film can be used as a protective coating for polycarbonate. The optimum conditions for the deposition of an almost stress-free film were 17% of HMDSO and dc bias voltage of ?240?V. The film hardness and elastic modulus were 10?GPa and 75?GPa, respectively. The refractive index at 600?nm was 1.5 and the extinction coefficient decreased from 0.02 at 240?nm down to zero at 600?nm.The films deposited from HMDSO/CH4 and HMDSO/CH4/H2 mixtures exhibited the attractive properties of DLC films with the partial elimination of some of their drawbacks, such as absorption in the visible and a high intrinsic stress. The optimum concentration of the HMDSO was approximately 21%. Under these conditions the concentration of SiOx in the films was approximately 9?at.%. The film hardness and elastic modulus were above 22?GPa and 120?GPa, respectively.

Deposition of hard thin films from HMDSO in atmospheric pressure dielectric barrier discharge

An atmospheric pressure dielectric barrier discharge burning in nitrogen with a small admixture of hexamethyldisiloxane (HMDSO) was used for the deposition of thin organosilicon films. The thin films were deposited on glass, silicon and polycarbonate substrates, and the substrate temperature during the deposition process was increased up to values within the range 25 - 150 C in order to obtain hard SiOx-like thin films.

Protection Coatings for Polycarbonates based on PECVD from Organosilicon Feeds

Abstract We deposited protective films by plasma enhanced chemical vapour deposition (13.56 MHz) on polycarbonate and silicon substrates from tetraethoxysiloxan or hexamethydisiloxan mixed with oxygen and argon. The thickness and optical parameters of the films were calculated from the measured reflectance in the visible. The film growth rate changed from 2 to 50 nm/min. In most of the deposition conditions used, the films were nonabsorbing in the visible. The Vickers microhardness of the system film-polycarbonate was measured in the load range 5–1000 mN. The calculated film hardness was from 500–1000 HV. Three factors were essential for higher film hardness in addition to a higher deposition rate: the ratio of the monomer flow rate to the oxygen one was higher than ten, slightly elevated substrate temperature to about 70 °C and negative bias from − 200 V.

Correlation between SiOx content and properties of DLC:SiOx films prepared by PECVD

Hard diamond like carbon (DLC) films with an addition of SiOx were deposited in capacitively coupled rf discharges from a mixture of methane and hexamethyldisiloxane (HMDSO). The flow rate of HMDSO was changed in order to vary the SiOx content in the films. Complete atomic composition of the films was determined by Rutherford backscattering spectroscopy combined with elastic recoil detection analysis. The thickness and the optical properties were obtained from the ellipsometric measurements. The mechanical properties were studied by a depth sensing indentation technique using Fischerscope H100 tester. The O/Si ratio in DLC:SiOx films was 0.286 and the content of SiOx increased with the HMDSO-to-methane flow rate ratio q. The DLC:SiOx films were close to DLC films as concerning the optical properties in the uv/visible and the high hardness if q was maximum 0.25. However, the compressive stress in the films was reduced, the film fracture toughness was improved and the deposition rate increased.

Optical properties of diamond-like carbon films containing SiOx

In this paper the optical properties of amorphous DLC films containing SiOx (DLC:SiOx) prepared by plasma enhanced chemical vapour deposition are studied. For this study a combined optical method based on simultaneous interpretation of experimental data obtained within variable angle spectroscopic ellipsometry and near-normal spectroscopic reflectometry is used. The interpretation of these combined experimental data is performed using a new empirical dispersion model of the optical constants characterizing the films under investigation. This dispersion model is based on parameterizing the density of the electronic states belonging to both the valence and conduction bands. It is shown that there are the strong differences between spectral dependences of the optical constants of the DLC films on the one hand and DLC:SiOx films on the other hand. Further, it is shown that the absorption of the DLC:SiOx films is smaller than the absorption of the pure DLC films in the visible. This is explained by the fact that the density of the pi electrons inside the DLC:SiOx films is lower than the density of these electrons in the pure DLC films. It is also found that the existence of small amounts of the silicon and oxygen impurities contained in the DLC films strongly influence their optical properties.

THE INFLUENCE OF SUBSTRATE EMISSIVITY ON PLASMA ENHANCED CVD OF DIAMOND-LIKE CARBON FILMS

In a planar capacitively coupled RF reactor we deposited diamond-like carbon (DLC) films from the mixture of methane and argon. The self biased electrode was in a poor thermal contact with walls of the reactor, neither water cooled nor electrical heated by a special external circuit. The heating of the electrode was caused mainly by the ion bombardment. We measured the temperatures of a self biased electrode and silicon substrates placed on it with Raytek Thermalert pyrometer in the temperature range 0–500°C. The temperatures were continuously increasing even during the longest deposition time of 120 min and differed for the electrode and the silicons of different specific resistances correlated to their emissivities. Ellipsometric and reflectance measurements of films deposited on two different silicon substrates of different emissivities were carried out. We discussed appropriate models for a film optical characterisation and found that apart a transient layer the studied films were homogeneous. Their deposition rate depended significantly on the silicon emissivities because of the different temperatures. The influence of the silicon substrate emissivity on the mechanical properties of DLC films was studied by means of Vickers microhardness tester.